1. Field of the Invention
The present invention relates to a plasma display panel (PDP) apparatus and a method for driving the same and, more particularly, to a PDP apparatus capable of protecting an element of a driving circuit and a discharge cell by securing time for activating the element by applying a reset waveform and a modified sustain waveform during at least one or more sub-fields right after power is applied to the panel, and a method of driving the same.
2. Description of the Related Art
A plasma display apparatus is an apparatus in which discharge cells are formed between a rear substrate with barrier ribs formed thereon and a front substrate facing the rear substrate, and when an inert gas inside each discharge cell is discharged by a high frequency voltage, vacuum ultraviolet rays are generated to illuminate phosphor to thereby allow displaying of images.
FIG. 1 is a perspective view showing the structure of a general PDP, and FIG. 2 is a sectional view showing a discharge cell of the general PDP.
To begin with, discharge cells are formed by a plurality of barrier ribs 24 separating a discharge space on a rear substrate 18 facing a front substrate 10.
An address electrode X is formed on the rear substrate 18, and a scan electrode Y and a sustain electrode Z are formed as a pair on the front substrate 10. The address electrode X crosses the other electrodes Y and Z, and in this respect, the rear substrate 18 in FIG. 2 is shown as having been rotated by 90° for the sake of explanation.
A dielectric layer 22 for accumulating wall charges is formed on the rear substrate 18 with the address electrode X formed thereon.
The barrier ribs 24 are formed on the dielectric layer 22 to define a discharge space therebetween and prevent a leakage of ultraviolet rays and visible light generated by a discharge to an adjacent discharge cell. Phosphor 26 is coated on the surface of the dielectric layer 22 and on the surface of the barrier ribs 24.
Because an inert gas is injected into the discharge space, the phosphor 26 is excited by the ultraviolet rays generated during a gas discharge to generate one of red, green and blue visible light.
The scan electrode Y and the sustain electrode Z formed on the front substrate 10 include transparent electrodes 12Y and 12Z and bus electrodes 13Y and 13Z, respectively, and cross the address electrode 12X. A dielectric layer 14 and a protective film 16 are formed to cover the scan electrode Y and the sustain electrode Z.
The discharge cell with such a structure is selected by a facing discharge formed between the address electrode X and the scan electrode Y, and the discharge is sustained by a surface discharge between the scan electrode Y and the sustain electrode Z, to thus emit visible light.
The scan electrode Y and the sustain electrode Z include the transparent electrodes 12Y and 12Z and the bus electrodes 13Y and 13Z having the smaller width than the transparent electrodes 12Y and 12Z and formed on one edge portion of the transparent electrodes 12Y and 12Z, respectively.
FIG. 3 shows a frame of the general PDP and FIG. 4 is a view showing waveforms according to a method for driving a PDP in accordance with a related art.
With reference to FIG. 3, in the plasma display panel, in order to represent gray levels of an image, one frame is divided into several sub-fields each having a different number of times of illumination and driven according to time division. Each sub-field (SF1˜SF8) includes a reset period (RPD) for initializing wall charges in the discharge cell, an address period (APD) for selecting a scan line and then selecting a discharge cell from the selected scan line, and a sustain period (SPD) for implementing gray levels according to the number of times that a sustain discharge occurs.
Gray levels implemented in the sub-fields including the reset period (RPD), the address period (APD) and the sustain period (SPD) are accumulated during one frame, and in case where an image is represented with 256 gray levels, as shown in FIG. 3, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields (SF1 to SF8) and each sub-field represents 2n (n=0, 1, 2, 3, 4, 5, 6, 7) gray levels.
Driving waveforms in a sub-field will now be described with reference to FIG. 4. A reset waveform (RP) supplied to the scan electrode (Y) during the reset period (RPD) includes a set-up waveform rising in a ramp form and a set-down waveform falling in the ramp form. As a voltage of the panel is increased by the set-up waveform, a reset discharge occurs and wall charges are formed at the dielectric layer 14. And, as the voltage of the panel is decreased by the set-down waveform, some unnecessary wall charges are erased.
During the address period (APD), a scan waveform (SP) having a negative (−) scan voltage (Vy) is supplied to the scan electrode (Y) and, at the same time, a data waveform (DP) is supplied to the address electrode (X), to make an address discharge occur.
During the sustain period (SPD), sustain waveforms SusPz and SusPy having repeated high and low potential voltage levels are alternately supplied to the scan electrode (Y) and the sustain electrode (Z), to make a sustain discharge occur.
Meanwhile, an energy recovery unit, provided in a scan driver and a sustain driver which apply driving waveforms to the scan electrode (Y) and the sustain electrode (Z), respectively, recovers energy from the panel during the sustain period (SPD) and re-supplies it during the sustain period (SPD). Thus, when the panel is initiated to be driven after having been sustained in an OFF state for a long time, a panel voltage cannot be recovered by the energy recovery unit, so quality of a displayed image is degraded due to a weak sustain discharge during the sustain period right after the initiation of the driving of the panel.
In addition, when the panel is initiated to be driven after having been sustained in the OFF state for a long time, a high voltage is suddenly supplied to an element of a circuit for driving the PDP and the discharge cell, the element is inevitably damaged.
In more detail, generally, an element mounted in the driving circuit or in the discharge cell needs a certain preliminary time for allowing the element to be activated in a stable state. Thus, in this respect, if a high voltage is applied to the element without having such a preliminary time, the element would be suddenly turned to the activated state, and thus, electrical/physical characteristics of the element are changed or damaged.
In particular, as shown in FIG. 5, there is a high possibility that the element in the driving circuit and in the discharge cell is damaged due to a voltage difference (Vxy) between the scan electrode (Y) and the sustain electrode (Z) during the sustain period (SPD) during which the sustain waveforms SusPz and SusPy are alternately applied to both electrodes.
Namely, when the power supply to and power cutoff from the PDP are repeated or when the waveforms having repeated rising and falling levels like the sustain waveforms SusPz and SusPy are supplied, not only the electrical/physical characteristics of the element of the driving circuit and the discharge cell would be changed but also a lifespan of the PDP would be reduced.